It is desirable in many applications to have a burner which will operate using a plurality of fuels. Such a burner is described and claimed in Reissue U.S. Pat. No. 28,679 naming the same inventor as named in the present application. The use of a multi-fuel burner is desirable because it may be operated with fuel as is readily available in the operating environment where the burner is utilized. For example, in the high north, construction and mining equipment may operated with diesel fuel. It is convenient to use such a fuel for operating the burner.
The burner illustrated and disclosed in Reissue Pat. No. 28,679 and in U.S. Pat. No. 5,102,328, however, utilize in the first instance a round flame grid and, in the second instance, a cylindrical flame grid which are convenient for the particular applications under which they may be used. In other applications, however, it is convenient to utilize a flame grid having a different configuration which may be designed and manufactured for far less expense and which may be used, for example, for water heating and for oven heating, which oven may be used in a field kitchen by the military. A furnace may also utilize the burner which furnace distributes the hot air by using appropriate ducting.
Heretofore, the multi-fuel burner according to the aforementioned patents has used an ignition electrode to provide for the initial combustion of the atomized liquid fuel which is emitted from the nozzle by the venturi action of the primary air in the nozzle. Ignition electrodes, however, have a gap in which the distance is critical. The tips of such electrodes can also burn off until the electrode eventually becomes inoperable and a relatively high amount of power is required to form the spark on the electrode. Thus, relatively high maintenance is required to keep the ignition electrode in optimum condition and replacement is, of course, required from time to time.
Although igniters have been used with gaseous systems such as propane as described in U.S. Pat. No. 3,875,477, it has not been contemplated that an igniter may be used with atomized liquid fuels. Although propane is stored in a liquid form, when the pressure is released on the liquid, the propane is ejected by the nozzle in gaseous form. The propane will be ignited when it passes over the igniter.
The place of introduction of secondary air is important. For example, if it is desired that combustion occur on an external grid rather than internally of the burner tube, the secondary air is added at a location where it supports combustion on the grid and not within the burner tube.
In our pending U.S. patent application Ser. No. 08/272,819 filed Jul. 11, 1994 and now allowed, the contents of which are incorporated herein by reference, there is disclosed an infrared burner with an air aspirated nozzle, a zero pressure regulator which regulates the fuel flow from the fuel tank to the air aspirated nozzle and a fuel pump which regulates the fuel flow to the air aspirated nozzle. The teachings of the '819 application are useful in many applications and the apparatus there disclosed works satisfactorily for those applications.
However, where there is a larger range of operating energy required, it is difficult to provide a decrease in fuel flow at the low fire operation using a fuel pump. The fuel pump does not operate properly at the low fire operation to allow a reduction of fuel flow sufficient to obtain the low fire operation. In addition, the fuel pump provides pulsed fuel flow. At higher energy requirements, the fuel flow provided by the fuel pump is sufficient to allow consistent ignition of the fuel. But at low fire operation, the pulsed fuel flow is exaggerated with the result that fuel combustion is somewhat inconsistent. In addition, by reducing the power to the fuel pump to obtain the decrease in fuel flow, the fuel pump would simply quit operating under certain power applications.
In addition to the operating difficulties at low fire, the fuel pump of the '819 application is controlled electronically. The burner according to the present application and the '819 application is required to be used in field facilities where it is not treated with delicate care. Electronic controls can easily be damaged and, of course, electronic controls are complex and costly.